The present invention relates to stabilizing fuel by deoxygenation, and more particularly to deoxygenation through a composite oxygen permeable membrane which minimizes fuel absorption.
Jet fuel is often utilized in aircraft as a coolant for various aircraft systems. The presence of dissolved oxygen in hydrocarbon jet fuels may be objectionable because the oxygen supports oxidation reactions that yield undesirable by-products. Dissolution of air in jet fuel results in an approximately 70 ppm oxygen concentration. When aerated fuel is heated between 350° F. and 850° F. the oxygen initiates free radical reactions of the fuel resulting in deposits commonly referred to as “coke” or “coking.” Coke may be detrimental to the fuel lines and may inhibit combustion. The formation of such deposits may impair the normal functioning of a fuel system, either with respect to an intended heat exchange function or the efficient injection of fuel.
Various conventional fuel deoxygenation techniques are currently utilized to deoxygenate fuel. Typically, lowering the oxygen concentration to approximately 2 ppm is sufficient to overcome the coking problem.
One conventional Fuel Stabilization Unit (FSU) utilized in aircraft removes oxygen from jet fuel by producing an oxygen partial pressure gradient across an oxygen permeable membrane. The membrane is in contact with fuel flow and is supported on a porous backing plate such that oxygen may be extracted from the fuel.
Although quite effective, a very small amount of fuel may leak through the 6-12 angstrom-sized pores of the oxygen permeable membrane. The rate of fuel leakage is inversely proportional to the thickness of the membrane: however, the rate of oxygen removal is also inversely proportional to membrane thickness. Therefore, an increase in membrane thickness will reduce fuel leakages, but the increase will also proportionally reduce deoxygenation. However, minor fuel leakage may be detrimental in that, over a period of time, fuel may saturate the membrane, block the permeation of oxygen, and reduce deoxygenation efficiency thereof.